Silverfox From United Kingdom, joined Mar 2001, 1058 posts, RR: 0 Posted (10 years 8 months 2 weeks 17 hours ago) and read 1287 times:
When i flew a BA 747 i was in the rear facing seat. On the take off run, as the engines spooled up the intakes had a 'cloud' form inside them. it remained for about 10-15 secs (i will check on the video) before disappearing.
What caused this? is it a normal phenomenom, or just the weather conditions at the time?
I havent checked any other intakes as i am normally behind or adjacent to them.
Any ideas etc?
Silverfox From United Kingdom, joined Mar 2001, 1058 posts, RR: 0 Reply 2, posted (10 years 8 months 2 weeks 17 hours ago) and read 1272 times:
Not worried at all. just fascinated by it. I thought it might have something to do with weather conditions, just needed a confirm. very spectacular in my opinion.
Now we are going to get all the 'neds' looking backwards on takeoff!!
LZ-TLT From Germany, joined Apr 2001, 431 posts, RR: 0 Reply 4, posted (10 years 8 months 2 weeks 17 hours ago) and read 1255 times:
A common phenomenon when taking off in high humidity and/or low air temperatures.
As air is sucked into the jet intakes or passes the wing's leading edge, it has a high velocity relatively to the aircraft's parts(ie, engine intake, wing and so on). Since the high velocity produces high dynamic pressure(in means of elementary fluid mechanic), but the sum of the dynamic, static and hydrostatic pressure for a given fluid remains always constant(Bernoulli's equation) and the hydrostatic pressure of the atmosphere depends only on weight, the increase of dynamic pressure is compensated by a drop in static pressure. Lower static pressure means, the condensation threshold for dissolved water vapour sinks, so the water vapours in the air condensate and form this fascinating fog. The same happens over the wing's leading edge.
There are a lot of photos here at a.net where you can see the same thing. A breathtaking sight indeed.
Silverfox From United Kingdom, joined Mar 2001, 1058 posts, RR: 0 Reply 7, posted (10 years 8 months 1 week 6 days 15 hours ago) and read 1060 times:
Thanks for all the info, i knew about the vortex etc, but as i said it was the first time i had seen it on engines..still get a kick on the video watching it.
Thanks again
PW100 From Netherlands, joined Jan 2002, 1983 posts, RR: 10 Reply 8, posted (10 years 8 months 1 week 5 days 20 hours ago) and read 976 times:
LZ-TLT
Very comprehensive explanation indeed! Just one remark... it's valid only for subsonic flow. At supersonic flow it doesn't work no more. Nature's reaction to supersonic flow is the shockwave.
PW100
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